On average, new treatments perform better in clinical trials only slightly more often than existing treatments, according to a new systematic review published in The Cochrane Library. The fact that experimental treatments are not more effective may seem disappointing, but the authors of the review say their findings satisfy an important ethical requirement for clinical trials. Randomised trials compare the effects of one treatment to another. In a randomised trial patients are randomly allocated to different treatment groups to ensure that like will be compared with like. When a new treatment is being tested, it is hoped or even expected that it will be better than the established treatment with which it is being compared. These expectations lead to an ethical dilemma. If the researchers already know that one treatment is better, they would be knowingly allocating some people to an inferior treatment. If randomised trials are to be ethical, therefore, only half of new treatments should turn out to be better than existing ones.